Organic Light Emitting Devices (OLEDs) are Lambertian light emitters and, consequently, they emit light at all angles. When such Lambertian light emitters are used as lighting for a workspace, for example, at the ceiling of an office, glare may be become a problem. Glare is the sensation produced by bright areas within the field of view. The Lambertian light emitter may be seen directly within the field of view or may be seen as reflections, for example, on a computer display. Various national and international standards are defined to reduce the disadvantageous effect of glare. For example, a typical norm is that the light emitters, or luminaries comprising a light emitter, have to be designed to have a strong reduction of light emission at light emission angles higher than 60° such that not more than 1000 cd/m2 is emitted at light emission angles larger than 65°. The light emission angle is defined with respect to a vertical axis.
In an article of Hyouk Kwon et. al., “Micro lens Array Film with Full fill factor for enhancing outcoupling efficiency from OLED lighting”, Solid-State Sensors, Actuator and Microsystems Conference 2007 Transducers 2007 International, 10-14 Jun. 2007, pp 1091-1094, a solution for a better outcoupling of light from an OLED has been discussed. The article discloses a sheet with a Micro lens Array (MLA) that should be optically coupled to the light emitting surface of the OLED. The OLEDs with a MLA do not fulfill the typical glare norms.
In patent application WO2005/083317A1 is disclosed a translucent lighting panel which has at a light emitting surface protrusions of a specific shape which prevents the emission of light at relatively small angles to the plane of the panel and thus prevents glare. The protrusions have a pyramid shape or a conical shape. A surface of the translucent lighting panel, which is substantially opposite the light emitting surface, receives light from a light emitter and may be substantially flat.
Thus, it seems logical not to laminate the OLED with the MLA sheet of the cited article, but to laminate the OLED with the translucent lighting panel of the cited patent application in order to prevent glare and to obtain a better outcoupling of light. It is expected that the protrusions assist in the outcoupling of light, as the micro lenses do, and that the protrusions of the specific shape prevent the emission of light at relatively small angles to the plane of the panel. However, in evaluations it was found that the beamshaping effect of the sheet with protrusions of the specific shapes disappeared in this configuration and glare problems still exist with OLEDs laminated with the translucent lighting panel of the cited patent application.